1. Field of the Invention
The present invention relates to a technology for displaying computer generated holograms on such display medium as electronic display panel.
This application is based on Patent Application Nos. Hei 9-131531, Hei 9-131532, Hei 10-008161 and Hei 10-049093 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, one method of producing computer generated holograms is to express an object as a collection of point-light sources, and obtain holographic fringe patterns of the wavefronts by computation and display the resulting holograms using acousto-optical modulator or liquid crystal display. Acousto-optical modulator suffers from a disadvantage that only one-dimensional fringes (horizontal parallax only) can be expressed, but liquid crystal panels has advantages such as its capability to display two-dimensional images and the ease of altering the image electrically. However, because it is normally necessary to electrically control the gray levels of each pixel in the liquid crystal panel, manufacturing of finer pixel spacing is limited by the difficulties in control circuit fabrication and other factors. To display a hologram, it is basically necessary to provide fine resolution of higher then 1,000 lines/mm, but such fine resolutions are difficult to achieve in practice so that holograms can presently display only fairly coarse images.
That the image resolution and its dynamic range are limited when using electronic display devices, such as liquid crystal display, means in effect that there is an upper limit of spatial frequencies that can be displayed on such devices and it can display only 256 gray level. In other words, to display one object, it is necessary to be able to display a certain amount of high frequency components, but because of the low resolution of the display devices, it is difficult to clearly display several items on the same screen. This is because the limiting high frequency components and dynamic range for display one object overlaps those of another items, thereby resulting in destruction of the fringe patterns of the high frequency components. Technically, it leads to a lack of sufficient data to reproduce the item, resulting in high value of signal to noise (S/N) ratio, and thereby restricting the number of items displayable in one view, i.e., limiting the expressive capability of displaying the details of object information.
It is an aim of the present invention to provide a technology for displaying computer generated hologram images to enable to display more detailed shapes of a display object or a larger number of display objects than is possible by the conventional hologram display technology, even when using an electronic display apparatus, such as liquid crystal display, which has a limited image resolution and dynamic range capability.
The aim has been achieved in a method for computing fringe patterns of a display object comprised by items and displaying computer generated holograms. In this methodology, three-dimensional data of the display object are converted into computational data for fringe pattern generation, and a sampling rule for sampling computational data is determined and computational data are sampled according to a selected sampling rule. Wavefronts are generated by assuming that each position of sampled three-dimensional data has a light source and generates a wavefront, and fringe patterns generated by interference of computed wavefronts and a reference beam are obtained and stored as hologram images. The steps of sampling and generating a wavefront are repeated for all computational data. The plurality of hologram images thus generated are displayed successively using the display apparatus provided in the present invention, which is used in conjunction with the procedures that are provided through suitable recording media exemplified.
The method thus achieves the object of displaying more detailed shapes of an item or a larger number of items by distributing the holograms, produced by the steps presented above, over a plurality of moving picture frames by a sampling technique appropriate to the nature of the display object.
The aim has been achieved in another method that can produce hologram video of a display object. In the moving picture production methodology, three-dimensional data of the display object are input into a computer device and input data are classified or grouped according to attributes of the display object, and a plurality of fringe patterns are computed for each classified or grouped display object. The plurality of fringe patterns are respectively converted into a plurality of digital images, and the plurality of digital images are decomposed into individual bits to form bit images. Bit images obtained for each classified or grouped display object are synthesizing to produce moving pictures for display. The plurality of hologram images thus generated are displayed successively using the display apparatus provided in the present invention, which is used in conjunction with the procedures that are provided through suitable recording media exemplified.
The method thus achieves the aim of displaying a larger number of items while decreasing the number of items displayed in one frame by distributing the digital images of the fringe patterns of a plurality of items, produced by the steps presented above, over a plurality of scenes in moving pictures, defined by frames and fields, by a digital processing technique appropriate to the nature of the display object.